1. Field of the Invention
The present invention relates to a double-port energy storage system (ESS) and a control method thereof. More particularly, the present invention relates to the double-port energy storage system and the control method thereof for flexibly supplying various power qualities and simplifying the entire structure.
2. Description of the Related Art
FIG. 1 shows a schematic block diagram of a conventional energy storage system operated in a power storage state. Referring initially to FIG. 1, the conventional energy storage system 1 mainly includes a bidirectional power conversion circuit 11 and an electric energy storage facility 12. The bidirectional power conversion circuit 11 has an AC side and a DC side. The AC side of the bidirectional power conversion circuit 11 connects with a utility power source 10 via an AC switch 14 while the DC side of the bidirectional power conversion circuit 11 connects with the electric energy storage facility 12. The AC side of the bidirectional power conversion circuit 11 further connects with a load 13.
Still referring to FIG. 1, when the utility power source 10 stays within its normal tolerance and it is in an off-peak time period, for example, for an electric energy rate, the AC switch 14 is selectively switched on as a close state. Accordingly, an AC power supplied from the utility power source 10 is converted into a DC power by the bidirectional power conversion circuit 11 and the DC power is stored in the electric energy storage facility 12, as best shown in a lower dotted line and a directional arrow thereof in FIG. 1. The electric energy storage facility 12 comprises several batteries or DC power sources. The utility power source 10 does not further supply the AC power or any charging energy when the electric energy storage facility 12 is completely charged. In addition, the utility power source 10 will selectively supply the AC power into the load 13, as best shown in an upper dotted line and a directional arrow thereof in FIG. 1.
FIG. 2 shows a schematic block diagram of the conventional energy storage system, which corresponds to that in FIG. 1, operated in a power release state when the utility power stays within its normal tolerance. Referring to FIG. 2, when the utility power source 10 stays within its normal tolerance but it is in a peak time period, the AC switch 14 is selectively switched on as a close state. The utility power source 10 selectively supplies the AC power into the load 13, as best shown in an upper dotted line and a directional arrow thereof in FIG. 2. In addition, the electric energy storage facility 12 of the conventional energy storage system is changed into the power release state and a DC power of the electric energy storage facility 12 is converted into an AC power supplying to the load 13 via the bidirectional power conversion circuit 11, as best shown in a lower dotted line and a directional arrow thereof in FIG. 2. Accordingly, the electric energy storage facility 12, which stores electric energy during the off-peak time period, accomplishes supplying the power to the load 13 as a part of power consumption at the load 13.
FIG. 3 shows a schematic block diagram of the conventional energy storage system operated in another power release state, which corresponds to that in FIG. 2. Referring to FIG. 3, when the utility power source 10 is out of tolerance or failure, the AC switch 14 is selectively switched off as an open state to disconnect with the utility power source 10. The electric energy storage facility 12 of the conventional energy storage system is still operated in the power release state and the DC power of the electric energy storage facility 12 is still converted into the AC power supplying to the load 13 via the bidirectional power conversion circuit 11, as best shown in a dotted line and a directional arrow thereof in FIG. 3. Accordingly, the electric energy storage facility 12 supplies entire power requirement to the load 13.
For example, U.S. Pat. No. 7,911,187 entitled “Energy storage system”, discloses an energy storage system including a battery charger and energy storage devices. The battery charger is connected to a DC/AC current source. The energy storage devices are coupled between the battery charger and subsystems respectively. Each of the energy storage devices includes a magnetic capacitor (MCAP) and an over current protection device (OCPD). MCAPs are charged by the battery charger and supply the electric power to subsystems connected the energy storage devices. OCPDs detect current from MCAPs to subsystems and protect subsystems from excessive currents of voltages.
Another U.S. Patent Application Publication No. 20100327806 entitled “Monitoring cells in energy storage system”, discloses a system for monitoring an energy storage system composed of multiple cells connected in series has a chain of monitors including at least first and second monitors. The first monitor is configured for monitoring at least a first cell in the energy storage system to produce first monitored data. The second monitor is configured for monitoring at least a second cell in the energy storage system to produce second monitored data. The first monitor is further configured for transferring the first monitored data to the second monitor for delivery to a controller.
Another U.S. Patent Application Publication No. 20110296218 entitled “Battery management system, method of controlling the same, and energy storage system including the battery management system”, discloses a battery management system (BMS), a method of controlling the same, and an energy storage system including the battery management system. The BMS may reduce costs by stably supplying power to an insulating unit in a power-saving mode even when an isolator has no built-in direct current (DC)-DC converter.
However, the conventional energy storage system only provides a single AC port and a single function thereof but it fails to provide double AC ports and functions thereof. Disadvantageously, the functions and operations of the conventional energy storage system are however limited and inflexible. The above-mentioned patents and publications are incorporated herein by reference for purposes including, but not limited to, indicating the background of the present invention and illustrating the situation of the art.
As is described in greater detail below, the present invention intends to provide a double-port energy storage system and a control method thereof. A first AC port, a second AC port and a plurality of switches are arranged in the energy storage system on which to form double AC ports for supplying the stored power by controllably operating the switches. A first power quality (e.g. voltage or frequency) supplied at the first AC port depends on that of a utility power source and a second power quality supplied at the second AC port is independent from the utility power source such that the double-port energy storage system is capable of supplying various levels (or classifications) of power quality via the first AC port and the second AC port. Advantageously, the double-port energy storage system of the present invention is successful in flexibly supplying various levels (or classifications) of power quality. In addition, the double-port energy storage system of the present invention provided with two AC ports supplies various levels of power quality without installing two conventional single-port energy storage systems. Advantageously, the present invention successfully simplifies the entire structure of double-port energy storage systems.